Electric potential sensor

Abstract

The present invention provides an electric potential sensor for the measurement of potentials non-invasively. The sensor comprises at least one detection electrode arranged for capacitive coupling with a sample under test and for generating a measurement signal, and a sensor amplifier adapted to receive the measurement signal as input and to supply an amplified detection signal as output. Input impedance enhancing means are included for providing a high input impedance to the sensor amplifier for increasing the sensitivity of the electrode to reduced electric potentials, and a discrete pre-amplifier stage is arranged to co-operate with the sensor amplifier to reduce the input capacitance of the amplifier.

Description

TECHNICAL FIELD[0001]The present invention concerns electric potential sensors for use for the measurement of potentials non-invasively in a wide variety of applications, for example in the fields of medical diagnostics and biometric sensing.BACKGROUND OF THE INVENTION[0002]In order to create a sensitive electrodynamic measuring device, it is customary to provide a high input impedance and thereby reduce the power of the input signal required to operate the device. However, electronic circuits with a very high input impedance tend to be unstable, and so practical devices are usually a compromise between achieving the necessary degree of sensitivity, providing the desired input impedance and ensuring an acceptable degree of stability.[0003]In International Patent Application No. WO 03 / 048789, an electrodynamic sensor is disclosed in which different circuit techniques are combined to achieve several orders of magnitude improvement in sensitivity, by comparison with previously known el...

AI Technical Summary

Benefits of technology

The present invention provides a novel electric potential sensor that can accurately and non-invasively measure signals. It also enhances the signal to noise ratio by increasing the sensitivity of the electrode to reduced electric potentials. The sensor includes a detection electrode, a sensor amplifier, input impedance enhancing means, and a discrete pre-amplifier stage. The input impedance enhancing means may include a guard circuit, a bootstrapping circuit, a neutralization circuit, and supply rail drift correction, supply modulation, and offset correction for the sensor. The detection electrode may be surrounded by a conducting element connected to a zero reference potential to reduce effective source impedance. The invention also includes means for reducing the noise amplitude to increase the signal to noise ratio, such as a dc stability gain setting circuit, a noise matching circuit, and an enhanced bootstrap circuit.

Problems solved by technology

However, electronic circuits with a very high input impedance tend to be unstable, and so practical devices are usually a compromise between achieving the necessary degree of sensitivity, providing the desired input impedance and ensuring an acceptable degree of stability.

Whilst these features assist in providing a sensor with high input impedance and a relatively stable operation, nevertheless, in situations where there may be weak capacitive coupling to, or a signal of small amplitude generated by, a source or sample under test, noise problems may still remain and may inhibit or prevent accurate signal measurement.

In this case, the measurement signal received by the sensor is attenuated by the capacitive potential divider formed by the coupling capacitance and the input capacitance and may be difficult to capture.

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